Flavour inclusive, udsc and b fragmentation functions in unbiased jets, and flavour inclusive, udsc, b and gluon fragmentation functions in biased jets are measured in e+e- annihilations from data collected at centre-of-mass energies of 91.2, and 183-209 GeV with the OPAL detector at LEP. The unbiased jets are defined by hemispheres of inclusive hadronic events, while the biased jet measurements are based on three-jet events selected with jet algorithms. Several methods are employed to extract the fragmentation functions over a wide range of scales. Possible biases are studied in the results are obtained. The fragmentation functions are compared to results from lower energy e+e- experiments and with earlier LEP measurements and are found to be consistent. Scaling violations are observed and are found to be stronger for the fragmentation functions of gluon jets than for those of quarks. The measured fragmentation functions are compared to three recent theoretical next-to-leading order calculations and to the predictions of three Monte Carlo event generators. While the Monte Carlo models are in good agreement with the data, the theoretical predictions fail to describe the full set of results, in particular the b and gluon jet measurements.
The udsc jet fragmentation function in bins of $x_{\rm E}$ and scale. The scale denotes $Q_{\rm jet}$ for the biased jets and is given by the intervals, while it denotes $\sqrt{s}/2$ for the unbiased jets and is given by the single values. These data are displayed in Fig.7.
The b jet fragmentation function in bins of $x_{\rm E}$ and scale. The scale denotes $Q_{\rm jet}$ for the biased jets and is given by the intervals, while it denotes $\sqrt{s}/2$ for the unbiased jets and is given by the single values. These data are displayed in Fig. 8. In the region 0.48 $<x_{\rm E}<$ 0.90 and $Q_{\rm jet}=$ 30-70 GeV, no measurement was possible due to low statistics.
The gluon jet fragmentation functions in bins of $x_{\rm E}$ and scale $Q_{\rm jet}$ obtained from the biased jets using the b-tag method (BT). These data are displayed in Fig. 9. In the region 0.48 $<x_{\rm E}<$ 0.90 and $Q_{\rm jet}=$ 30-42 GeV for the b-tag method, no measurement was possible due to low statistics.
Elements of the spin density matrix for W bosons in e+e- -> W+W- -> qqln events are measured from data recorded by the OPAL detector at LEP. This information is used calculate polarised differential cross-sections and to search for CP-violating effects. Results are presented for W bosons produced in e+e- collisions with centre-of-mass energies between 183 GeV and 209 GeV. The average fraction of W bosons that are longitudinally polarised is found to be (23.9 +- 2.1 +- 1.1)% compared to a Standard Model prediction of (23.9 +- 0.1)%. All results are consistent with CP conservation.
The fraction of longitudinal polarization for leptonically and hadronically decaying W bosons. The average values for all the centre of mass energies and for both lepton and hadron decay combined are also given.
The luminosity weighted average over all the centre of mass energies of the diagonal elements of the RHO++ and RHO-- SDM as a function of the cosine of the angle of the W- boson for the leptonic decay channel.
The luminosity weighted average over all the centre of mass energies of the diagonal element of the RHO00 SDM as a function of the cosine of the angle of the W- boson for both leptonic and hadronic decay channels, and combined.
We present the first experimental results based on the jet boost algorithm, a technique to select unbiased samples of gluon jets in e+e- annihilations, i.e. gluon jets free of biases introduced by event selection or jet finding criteria. Our results are derived from hadronic Z0 decays observed with the OPAL detector at the LEP e+e- collider at CERN. First, we test the boost algorithm through studies with Herwig Monte Carlo events and find that it provides accurate measurements of the charged particle multiplicity distributions of unbiased gluon jets for jet energies larger than about 5 GeV, and of the jet particle energy spectra (fragmentation functions) for jet energies larger than about 14 GeV. Second, we apply the boost algorithm to our data to derive unbiased measurements of the gluon jet multiplicity distribution for energies between about 5 and 18 GeV, and of the gluon jet fragmentation function at 14 and 18 GeV. In conjunction with our earlier results at 40 GeV, we then test QCD calculations for the energy evolution of the distributions, specifically the mean and first two non-trivial normalized factorial moments of the multiplicity distribution, and the fragmentation function. The theoretical results are found to be in global agreement with the data, although the factorial moments are not well described for jet energies below about 14 GeV.
The charged particle multiplicity distribution of gluon jets, $n_{\rm gluon}^{\rm ch.}$, for $E_{\rm g}^*$$\,=\,$5.25, 5.98 and 6.98 GeV. The data have been corrected for detector acceptance and resolution, for event selection, and for gluon jet impurity.
The charged particle multiplicity distribution of gluon jets, $n_{\rm gluon}^{\rm ch.}$, for $E_{\rm g}^*$$\,=\,$8.43 and 10.92 GeV. The data have been corrected for detector acceptance and resolution, for event selection, and for gluon jet impurity.
The charged particle multiplicity distribution of gluon jets, $n_{\rm gluon}^{\rm ch.}$, for $E_{\rm g}^*$$\,=\,$14.24 and 17.72 GeV. The data have been corrected for detector acceptance and resolution, for event selection, and for gluon jet impurity.
Exclusive electroproduction of pi0 mesons on protons in the backward hemisphere has been studied at Q**2 = 1.0 GeV**2 by detecting protons in the forward direction in coincidence with scattered electrons from the 4 GeV electron beam in Jefferson Lab's Hall A. The data span the range of the total (gamma* p) center-of-mass energy W from the pion production threshold to W = 2.0 GeV. The differential cross sections sigma_T+epsilon*sigma_L, sigma_TL, and sigma_TT were separated from the azimuthal distribution and are presented together with the MAID and SAID parametrizations.
Cross section SIG(T) + EPSILON*SIG(L) for COS(THETA*) = -0.975.
Cross section SIG(T) + EPSILON*SIG(L) for COS(THETA*) = -0.925.
Cross section SIG(T) + EPSILON*SIG(L) for COS(THETA*) = -0.875.
Cross-section and angular distributions for hadronic and lepton-pair final states in e+e- collisions at centre-of-mass energies between 189 GeV and 209 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The measurements are used to determine the electromagnetic coupling constant alphaem at LEP2 energies. In addition, the results are used together with OPAL measurements at 91-183 GeV within the S-matrix formalism to determine the gamma-Z interference term and to make an almost model-independent measurement of the Z mass. Limits on extensions to the Standard Model described by effective four-fermion contact interactions or the addition of a heavy Z boson are also presented.
CM energy values.
Measured cross section for QUARK QUARKBAR (HADRON) production. The data are corrected to no interference between initial and final state radiation.
Measured cross section for MU+ MU- production. The data are corrected to no interference between initial and final state radiation.
We report on measurements of differential cross sections d sigma/d p_t for prompt charm meson production in p anti-p collisions at s**(1/2) = 1.96 TeV using 5.8 +/- 0.3 pb-1 of data from the CDF II detector at the Fermilab Tevatron. The data are collected with a new trigger that is sensitive to the long lifetime of hadrons containing heavy flavor. The charm meson cross sections are measured in the central rapidity region |y| \leq 1 in four fully reconstructed decay modes: D0 --> K- pi+, D*+ -> D0 pi+, D+ --> K- pi+ pi+, D+_s--> phi pi+, and their charge conjugates. The measured cross sections are compared to theoretical calculations.
Measured prompt charm production cross sections for ABS(YRAP) < 1. The branching ratios used are (D0:3.81 +- 0.09 PCT), (D+:2.57 +- 0.06 PCT),(D+:9.1 +- 0.6 PCT) and (D/S+:1.8 +- 0.5 PCT).
A study of Z-boson pair production in e+e- annihilation at center-of-mass energies between 190 GeV and 209 GeV is reported. Final states containing only leptons, (l+l-l+l- and l+l-nn), quark and lepton pairs, (qql+l-, qqnn) and only hadrons (qqqq) are considered. In all states with at least one Z boson decaying hadronically, lifetime, lepton and event-shape tags are used to separate bb pairs from qq final state. Limits on anomalous ZZgamma and ZZZ couplings are derived from the measured cross sections and from event kinematics using an optimal observable method. Limits on low scale gravity with large dimensions are derived from the cross sections and their dependence on polar angle.
The NC2 Z0-pair cross sections obtained from fits to the data.
For the first time at LEP the production of prompt photons is studied in the collisions of quasi-real photons using the OPAL data taken at e+e- centre-of-mass energies between 183 GeV and 209 GeV. The total inclusive production cross-section for isolated prompt photons in the kinematic range of photon transverse momentum larger than 3.0 GeV and absolute photon pseudorapidity less than 1 is determined to be 0.32 +- 0.04 (stat) +- 0.04 (sys) pb. Differential cross-sections are compared to the predictions of a next-to-leading-order (NLO) calculation.
The total prompt photon cross section in the kinematic range defined by theanti tagging condition.
Differential cross section in PT.
Differential cross section in ETARAP.
The Fermilab E866/NuSea Collaboration has measured the Drell-Yan dimuon cross sections in 800 GeV/$c$ $pp$ and $pd$ collisions. This represents the first measurement of the Drell-Yan cross section in $pp$ collisions over a broad kinematic region and the most extensive study to date of the Drell-Yan cross section in $pd$ collisions. The results indicate that recent global parton distribution fits provide a good description of the light antiquark sea in the nucleon over the Bjorken-$x$ range $0.03 \lesssim x < 0.15$, but overestimate the valence quark distributions as $x \to 1$.
Measurment of the scaling form of the MU+ MU- cross section in the XL range-0.05 to 0.05 from the hydrogen target.
Measurment of the scaling form of the MU+ MU- cross section in the XL range0.05 to 0.10 from the hydrogen target.
Measurment of the scaling form of the MU+ MU- cross section in the XL range0.10 to 0.15 from the hydrogen target.
Beam polarization asymmetries for the p(gamma,K+)Lambda and p(gamma,K+)sigma0 reactions are measured for the first time for Egamma=1.5-2.4 GeV and 0.6<cos(theta_cm(K+))<1.0 by using linearly polarized photons at the Laser-Electron-Photon facility at SPring-8 (LEPS). The observed asymmetries are positive and gradually increase with rising photon energy. The data are not consistent with theoretical predictions based on tree-level effective Lagrangian approaches. Including the new results in the development of the models is, therefore, crucial for understanding the reaction mechanism and to test the presence of baryon resonances which are predicted in quark models but are sofar undiscovered.
Measured beam asymmetries for the reaction GAMMA P --> K+ LAMBDA for beam energy 1.5 to 1.6.
Measured beam asymmetries for the reaction GAMMA P --> K+ LAMBDA for beam energy 1.6 to 1.7.
Measured beam asymmetries for the reaction GAMMA P --> K+ LAMBDA for beam energy 1.7 to 1.8.
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